Recently, research and development of heat-resistant materials has been actively conducted, and polyimides have attracted attention from the viewpoints of their excellent heat resistance and excellent dimensional stability. As such a polyimide, an aromatic polyimide “Kapton” is commercially available. This aromatic polyimide is a representative organic material developed in 1960's by DuPont USA, and has a heat resistance of the highest class among heat resistant polymers. The aromatic polyimide is known as a polymer material which can withstand high temperature of about 300° C. and even harsh space environment for a long period. However, such a wholly aromatic polyimide is colored in brown, because the intramolecular charge transfer (CT) occurs between an aromatic tetracarboxylic dianhydride unit and an aromatic diamine unit. Hence, the wholly aromatic polyimide cannot be used in applications where transparency is necessary (the printable electronics application, the flexible glass alternative application, the semiconductor resist application, and the like). For this reason, to produce a polyimide which can be used in applications where transparency is necessary, alicyclic polyimides which undergo no intramolecular CT and which have high light transmittance have been researched recently.
As such an alicyclic polyimide, for example, a polyimide is known which is obtained by using a combination of trans-1,4-cyclohexanediamine (t-CHDA) with pyromellitic anhydride (PMDA) or 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The alicyclic polyimide obtained by using a combination of t-CHDA with PMDA or BPDA is also known to have an extremely low linear expansion coefficient (for example, 10 ppm/° C. for a t-CHDA/PMDA system, and 10 ppm/° C. for a t-CHDA/BPDA system) (see SAISHIN PORIIMIDO—KISO TO OUYOU—(Current Polyimides—Fundamentals and Applications—), newly-revised edition, NTS INC., 2010, PP. 291 to 293 (NPL 1)). However, trans-1,4-cyclohexanediamine (t-CHDA) used for producing such an alicyclic polyimide is a monomer which forms an extremely hard salt at the initial stage of the polymerization with PMDA or BPDA, and hence is extremely difficult to polymerize in a usual manner. Accordingly, such a polyimide is not necessarily sufficient in terms of polymerizability, and is difficult to put into practical use.
Meanwhile, as another alicyclic polyimide, for example, International Publication No. WO2011/099518 (PTL 1) discloses a polyimide having a repeating unit represented by the following general formula:
[in the formula, Ra, Rb, and Rc each independently represent one selected from the group consisting of a hydrogen atom, alkyl groups having 1 to 10 carbon atoms, and a fluorine atom, Rd represents an aryl group having 6 to 40 carbon atoms, and n represents an integer of 0 to 12].